1. Field of the Invention
The present invention relates to a picture recording apparatus and, more particularly, to a method and apparatus for producing a hard copy of a color picture which is represented by video signals.
2. Description of the Prior Art
There has been known an electronic still camera system in which a picture is picked up by an electronic still camera or a television (TV) camera and then recorded on a video signal recording medium such as a magnetic video disk, or so-called video floppy, or a video tape. Meanwhile, there is an increasing demand for an apparatus capable of reproducing in the form of a hard copy a picture which is recorded on a video signal recording medium as mentioned, i.e., reproducing the picture as a visible one on a picture recording medium, such as a printing sheet of paper.
A recording apparatus with such a capability may be implemented with a system which displays a desired picture on a cathode ray tube (CRT) or any other picture display, then causes imaging optics to focus the picture being displayed onto a picture recording medium so as to expose the medium to the picture.
Where a color picture is to be recorded on a picture recording medium by reading video signals out of a video signal recording medium to display them on a CRT adapted for picture recording, a frame picture, or picture component, in each of three separated colors is formed and the resultant three picture components are superposed on each other in the same frame of the picture recording medium by additive color photography. For high quality reproduction of a picture, therefore, it is important that the three picture components are adequately balanced in color.
Recording schemes known in the art include one which uses a high luminance black-and-white CRT. In accordance with this particular scheme, pictures in three separate colors are selectively displayed on the screen of the CRT and passed through color filters which are respectively associated with the three separated colors, thereby exposing a picture recording medium. Specifically, such exposure is effected on the same frame of a picture recording medium for each of the three separated colors, whereby a color hard copy is produced by three-colors additive color photography.
To achieve a color hard copy with good color reproducibility by additive color photography as stated above, it is a prerequisite that the pictures in three separated-color components be focused onto a picture recording medium in an intended balance. This prerequisite cannot be met unless a picture capable of establishing an adequate relative color balance between the pictures of the three color components is produced on the screen of the CRT.
Generally, the screen of a black-and-white CRT is coated with a mixture of fluorescent substances having radiation characteristics which individually center around light components having particular wavelengths, e.g. red (R), green (G) and blue (B). Such substances provide the CRT with a flat radiation characteristic over the entire visible wavelength range. Usually, radiation characteristics of fluorescent substances are significantly temperature dependent and, moreover, the temperature characteristic in most cases differs from one emission wavelength range to another.
Assume that three separated-color picture components are sequentially reproduced on a screen, or a mixture of fluorescent substances having radiation characteristics which are different in temperature characteristic from each other, so as to combine the picture components by additive color photography on a picture recording medium through their associated color filters. Such undesirably brings about unbalance between the three separated colors. Specifically, when the radiation characteristic of a blue fluorescent substance, for example, has been deteriorated at a certain temperature, emission of the blue component is reduced. In this condition, should video signals representative of a B component be fed to the CRT to expose a picture recording medium to the blue picture component through a blue filter, a picture completed, or hard copy, would appear with a B component which is less than the other color components due to the short B luminance.